The worst offenders tend to be ex-fundamentalists. I think that there are at last two reasons for this:

1) A lifetime of avoiding critical thought is not instantaneously undone by going through a deconversion experience. A lot of newly-minted atheists haven't yet acquired the habit of genuinely critical thought.

2) They have rejected an essentially stupid version of Christianity and they haven't yet appreciated that not all versions of Christianity are as stupid as the version they left.

I find bad responses to cosmological arguments on the forums I post on. There are many confident atheists, like myself, but the difference is that they are not well acquainted with arguments for theism. I find when a theist posts a cosmological argument they find online, most atheists respond by saying "Well what caused God?", despite that missing the whole point of the arguments.

I'm not talking about hypothetical situations. Rather, I'm talking about actual conversations that I have held where atheists miss the point of the arguments.